Fungi influenced corrosion on nitrocarburized multiphase 4340 steel

doi: 10.17563/rbav.v32i1-2.921
Fungi influenced corrosion on nitrocarburized multiphase 4340 steel
Corrosão em aço 4340 multifásico nitrocarburado influenciada por fungos
Sabrina de Moura Rovetta1,2, Antonio Jorge Abdalla2, Vladimir Henrique Baggio Scheid2,
Sonia Khouri1, Choiu Otani3, Walter Miyakawa2
Abstract
Corrosion on multiphase steels is strongly influenced by the iron content. On the other hand, thermochemical
surface treatments like plasma nitrocarburizing have been successfully used to enhance resistance to saltspray corrosion, but the literature about microbial influenced corrosion is still scarce. The aim of this
work was then to evaluate the biocorrosion influenced by the Penicillium candidum fungus on plasma
nitrocarburized multiphase 4340 steel, comparatively with the untreated steel. Small blocks of treated and
untreated metals were evaluated by SEM, AFM, and EDS, before and after the biocorrosion process. It was
observed that biocorrosion drastically affected the surface of the untreated 4340 steel while nitrocarburized
samples preserved their original aspect. Only 7% of oxide content was detected in the nitrocarburized steel
against 32% in the untreated metal. It was concluded that plasma nitrocarburing was effective to improve
biocorrosion resistance of multiphase 4340 steel, and consequently, this treatment should be also tested with
other microorganisms and in other metals and alloys used in the aerospace and aviation industries.
Keywords: Biocorrosion; Fungi; Penicillium candidum; 4340 steel; AFM.
Resumo
Corrosão em aços multifásicos é fortemente influenciada pelo teor de ferro. Por outro lado, os tratamentos de
superfície termoquímicos como a nitrocarburação a plasma têm sido utilizados com sucesso para aumentar
a resistência à corrosão salt-spray, mas a literatura sobre a corrosão influenciada por microorganismos
ainda é escassa. O objetivo deste trabalho foi avaliar a biocorrosão influenciada pelo fungo Penicillium
candidum em aço multifásico 4340 após o tratamento de nitrocarburação a plasma comparado com o
aço sem tratamento. Pequenos blocos de aço com e sem tratamento foram avaliadas por SEM, AFM, e
EDS, antes e depois do processo de biocorrosão. Observou-se que a biocorrosão afetou drasticamente a
superfície do aço 4340 sem tratamento, enquanto as amostras nitrocarburadas teve o seu aspecto original
preservado. Foi detectado apenas 7% de teor de óxido no aço nitrocarburado contra 32% no aço não
tratado. Concluiu-se que a nitrocarburação a plasma foi eficaz para melhorar a resistência a biocorrosão
de aço multifásico 4340, e, consequentemente, este tratamento deve ser testado com outros microorganismos
e em outros metais e ligas utilizadas na indústria aeroespacial e de aviação.
Palavras-chave: Biocorrosão; Fungos; Penicillium candidum; Aço 4340; AFM.
Universidade do Vale do Paraíba – São José dos Campos/SP – Brazil
Instituto de Estudos Avançados – São José dos Campos/SP – Brazil
3
Instituto Tecnológico de Aeronáutica – São José dos Campos/SP – Brazil
Autor correspondente: Antonio Jorge Abdalla. Email: [email protected]
1
2
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Rovetta, S.M. et al.
Introduction
Materials and Methods
Multiphase steels are widely used in industry, usually
in structural applications for automotive, aerospace and
defense industries. However, despite the high technology involved in their production, multiphase steels are
susceptible to corrosion, mainly due to the significant
iron content. Thermochemical surface treatments as
plasma nitrocarburizing has been considered effective
to enhance some specific properties such as corrosion
resistance, hardness, friction wear, fatigue life(1-4), and in
fact, improvement on corrosion resistance and high surface hardness have been reported after these treatments(4).
However, the effects of microorganisms on multiphase
steels corrosion processes are scarcely studied.
Biocorrosion is the term commonly used to designate
an electrochemical process of metal dissolution due to the
presence of bacteria, microalgae, and fungi(1), that act as a
consortium of microorganisms(1). In this microbiologically
influenced process, metabolites and acidic by-products
alter the metal-solution interface, initiating, facilitating
or enhancing the corrosion process.
Many investigations have focused in microorganisms
of jet fuel systems(7-9), where both bacteria and fungi are
usually found. However, fungal growth has also been
observed in aircrafts passenger compartments(10), where
biocorrosion is also a matter of concern.
Fungi(5,11) are eukaryotic microorganisms, with a thick
and rigid cellular wall. The filamentous fungi growth
is ramified (mycelium) in single tubular multinucleate
structures (hyphae), originated from the germination of
reproductive spores. Morphologically more complex compared with the bacteria cells, the vegetative mycelium is
responsible for the fungi adherence in solid substrates,
while spores are formed in aerial hyphae.
The filamentous fungus Penicillium candidum used
in this work belongs to the saprophytic specie. During
their life-cycle, the P. candidum hydrolyzes ester bonds
to produce mono- and diacylglycerols, glycerol, and
organic and free fatty acids(12,13), which are corrosive
substances. This fungus was chosen because it has
been implicated in corrosion processes as much as
the genus Aspergillus(14-16).
The aim of this work was to evaluate the biocorrosion
on plasma nitrocarburized multiphase 4340 steel influenced by the fungi Penicillium candidum, comparatively
with the untreated 4340 steel.
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Sample preparation
Coupons (5 mm x 5 mm x 3 mm) were cut from a
plate of AISI 4340 steel. Five pieces were metallographically polished and acid-etched with 5% Nital solution for
10 seconds. Another set of coupons have their surfaces
nitrocarburized in a DC-pulsed plasma discharge, in a
75% N2, 23.5% H2 and 1.5% CH4 atmosphere, for three
hours, at temperature of 500ºC. Both treated and untreated
coupons have their surfaces evaluated by SEM-scanning
electron microscopy (LEO 1460Vp, Carl Zeiss, USA)
and by AFM-atomic force microscopy (SPM 9500J3,
Shimadzu, Japan), in contact mode, using conventional SiNi probes. Surface chemical microanalyses were
also performed by EDS-energy dispersive spectroscopy
(X-MAX EDS, Oxford Instruments, UK).
Biocorrosion
Lyophilized P. candidum (PC-TT033, CHR HASEN,
Denmark) was revitalized in sterile distilled water and
a pure culture was grown in Sabouraud Dextrose agar
(Himedia, India). From this pure culture, a fungal spore
suspension (1.50 x 105 spores/ml) was prepared in a glass
tube with sterile distilled water. Next, a set of glass tubes
with 3 ml of Sabouraud Dextrose broth (Himedia, India)
was inoculated with 100 μl of the prepared spore suspension. One coupon was immersed in each tube. The tubes
were kept at a constant temperature of 25ºC for 14 days.
After this incubation period, samples were evaluated using
the same techniques (SEM, AFM and EDS).
Results and Discussion
Figure 1a shows a characteristic image of the untreated
4340 steel surface obtained by SEM. Typical cementite
microstructures (needle-shaped Fe3C) can be seen over
the ferrite matrix (a-Fe, dark regions). Some bainite plates
can also be visualized (dashed white circles). It is important to notice that after the plasma nitrocarburizing, these
microstructures could no longer be identified (Fig. 1b).
Representative AFM bi-dimensional images with
40 µm x 40 µm of scanning area of the same untreated
4340 steel samples are presented in Fig. 2. In addition
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Fungi influenced corrosion on nitrocarburized multiphase 4340 steel
to the microstructures visualization (needle-shaped
cementite, dark regions of ferrite matrix and bainite plates, indicated by dashed circles), these images displayed quantitative information about height distribution
(right side of each micrograph). In Fig. 2a, the highest
peak of the cementite structure is about 225 nm far from the
deepest region of the a-ferrite matrix. In Fig. 2b, the
value 1.11 mm is the distance between the scratch bottom and the highest peak hill on the scratch edge.
Biocorrosion produced morphological alterations in the
untreated steel, easily identified by SEM. It can be observed
in Fig. 3a, some pits (cavities on the surface, indicated by
the smaller arrows) and also new structures (clear region,
indicated by the larger arrow). The EDS microanalysis
on these new structures revealed high contents of oxygen
(32% in weight), which has not been detected in the metal
before biocorrosion. This result strongly suggests that oxide
formation originated these new morphological structures.
As can be seen in Fig. 3b, the surface of a nitrocarburized 4340 steel after the biocorrosion process showed no
significant morphological alterations due to biocorrosion.
In addition, the EDS microanalysis on the nitrocarburized
4340 steel has detected only 7% of oxygen content after
biocorrosion. These results supported the finding that nitrocarburizing treatment of the metal is also an effective protection against biocorrosion.
Figure 2. Bi-dimensional visualization of atomic
force micrographs of (a) untreated and
(b) nitrocarburized 4340 steel.
Figure 3. Scanning electron micrographs of
(a) untreated (indicating biological corrosion)
and (b) nitrocarburized 4340 steel.
Figure 1. Scanning electron micrographs of
(a) untreated and (b) nitrocarburized 4340 steel.
Figure 4 shows AFM images of untreated and treated
steels after biocorrosion. In Fig. 4a, in addition to some
pits of corrosion (white arrows), it can be seen that all the
structures have lost their original morphology. Topography
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Rovetta, S.M. et al.
also changed drastically, increasing the height distribution scale to 663 nm. On the other hand, Fig. 4b corroborates Fig. 3b: no appreciable changes in morphology
and topography of the nitrocarburized steel surface were
measured by AFM after biocorrosion.
014/08), to FAPESP (grant #2014/05884-7), to Instituto
Tecnológico de Aeronáutica, for the AFM facility, and to
NUFABI – UNIVAP, for the microbiology infrastructure.
Referências
1. Baggio-Scheid, V.H.; Abdalla, A.J.; Vasconcelos, G., Plasma
Nitrocarburing and Laser Hardening Duplex Treatment of
AISI 4340 Steel, In: International Conference on Metallurgical
Coating and Thin Films, Proc. of the CMCOTF-2009, San
Diego, EUA, 2009.
2. Abdalla, A.J.; Carrer, I.R.; Barboza, M.J.R.; Moura Neto,
C., Estudo de fluência em aços 4340 com diferentes
microestruturas e tratamento de carbonitretação a plasma.
Anais do 19 Congresso Brasileiro de Engenharia e Ciência
de Materiais, November 25-29, 2010, Campos do Jordão,
SP, ref. 317-045. Available in http://www.cbecimat.com.
br/detalhes.asp?Id=886, accessed in July 18th, 2011.
3. Ranieri, A.; Scheid, V.H.B.; Suzuki,P.A; Abdalla, A.J., Plasma
nitrocarburizing treatment of 4340 steel. Proc. of the COBEM
2009 - International Congress of Mechanical Engineering,
Gramado, RS, 01 2009, pp. 01-06.
4. Abdalla, A.J.; Baggio-Scheid, V.H., Tratamentos termoquímicos a plasma em aços carbono. Corros. Prot. Mater.,
25 (2006) 92-96.
Figure 4. bi-dimensional visualization of atomic
force micrographs of untreated (a) and
treated (b) 4340 steel after biocorrosion.
Conclusion
Biocorrosion influenced by Penicillium candidum
resulted in severe surface deterioration on untreated 4340
steel, with pits and oxide formation. However, no noteworthy morphological and topographical changes were
observed in the nitrocarburized steel coupons.
The plasma nitrocarburizing treatment on the multiphase 4340 steel was also effective to improve the
resistance against biocorrosion by P. candidum fungi,
suggesting that it should be tested with other microorganisms and other metals and alloys used in the aerospace and aviation industries.
10
5. Videla, H.A., Manual of biocorrosion. 1rst ed., CRC
Press, Inc., 1996.
6. Costerton, J.W.; Geesey, G.G., The microbial ecology
of surface colonization and of consequent corrosion. In
Biologically induced corrosion, ed. S. C. Dexter. National
Association of Corrosion Engineers, Houston, TX, 223232, apud Videla, H. A., Microbially induced corrosion:
an updated overview. Int. Biodet. & Biodegrad., 48
(2001) 176-201.
7. Rajasekaranr, A.; Ting,Y.P., Microbial corrosion of aluminum 2024 aeronautical alloy by hydrocarbon degrading
bacteria Bacillus cereus ACE4 and Serratia marcescens
ACE2. Ind. Eng. Chem. Res., 49 (2010) 6054–6061.
8. Buddie, A.G.; Bridge, P.D.; Kelley,J.; Ryan, M.J., Candida
keroseneae sp. nov., a novel contaminant of aviation
kerosene. Lett. Appl. Microbiol., 52 (2010) 70–75.
9. Edmonds, P.; Cooney, J.J., Identification of microorganisms
isolated from jet fuel systems. Appl. Microbiol., 15 (1967)
411-416.
Acknowledgements
10. Little, B.J.; Lee, J.S., Microbiologically Influenced Corrosion.
Hoboken, N. J., USA, John Wiley and Sons, 2007.
To CNPq for the PIBIC/CNPq-IEAv grant, to Capes
for the project financial support (Capes Pró-Defesa
11. Papagianni, M., Fungal morphology and metabolite
production in submerged mycelial processes. Biotechnol.
Adv., 22 (2004) 189–259.
Revista Brasileira de Aplicações de Vacu2, v.30 n.1-2, 2013 7-11
Fungi influenced corrosion on nitrocarburized multiphase 4340 steel
12. Ruiz, B.; Farré, A.; Langley, E.; Masso, F.; Sánchez, S.,
Purification and Characterization of an Extracellular Lipase
from Penicillium candidum. Lipids 36 (2001), 283–289.
13. Ortiz-Vásquez, E.; Granadis-Baez, M.; Rivera-Muñoz,
G., Effect of culture conditions on lipolytic enzime
production by Pnicillium candidum in a solid state
fermentation. Biotechnol. Adv., 11 (1993) 409–416.
14. Videla, H. A., Biotecnologia- Corrosão microbiológica.
1rst ed., Edgard Blücher Ltda, São Paulo, 1986.
15. Silva, A. M.A.; Santiago, T. M.; Alves, C.R.; Guedes,
M.I.F.; Freire, J.A.K.; Vieira, R.H.S.F.; Da Silva, R.C.B.,
An evaluation of the corrosion behavior of aluminum
surfaces in presence of fungi using atomic force
microscopy and other tests. Anti-corrosion Methods and
Materials, 54 (2007) 289-293.
16. Smirnov, V.F.; Belov, D.V.; Sokolova, T N.; Kuzina, O.V.;
Kartashov, V.R., Microbiological corrosion of aluminum
alloys. Applied Biochemistry and Microbiology, 44
(2008) 192-196.
Revista Brasileira de Aplicações de Vácuo, v.32 n.1-2, 2013 7-11
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